Depression has become a common and frequently-occurring disease in modern society, whose incidence is still rising. It is featured by emotional distress, waning interest, retardation of thinking, and reduction of words and actions, and patients with major depression may have the ideas of world-weariness or suicide. Such disease will cause pain to patients and their families and loss to the society which are unmatched by many other diseases. According to the report from World Health Organization (WHO), affective disorder has now become the world's fourth-largest disease, and the patients suffering from depression have amounted to 340 million people worldwide. At present, the incidence of depression in China is about 4% and at least 26 million people have depression, causing the total economic burden of RMB 62.2 billion. In America, it is estimated that 17 million people are suffering from depression and 3 million people are attacked by manic depression, making the cost of treating affective disorder reach as high as USD 44 billion a year (USD 43 billion for coronary heart disease). Over the past 40 years of research on affective disorder, its high incidence and mortality are particularly striking; according to report, the suicide rate reaches up to over 10%, and every year 250,000 people commit suicide in China. Currently, the main drug used for treating depression is serotonin reuptake inhibitor (SRI), etc., which however has disadvantages such as slow onset of action, narrow effect spectrum, big side effects, and easy relapse after drug withdrawal. Now, it is in urgent need of more effective drugs and treatment methods with fast onset of action and small side effects in the field of antidepressant drugs.
The used antidepressant drugs so far have many weaknesses, for example, the shortcomings of currently used 3 kinds of antidepressant drugs, namely monoamine oxidase inhibitors, tricyclic antidepressants and heterocyclic antidepressants, mostly include slow onset of action, narrow antidepressant spectrum, relatively large side effects and easy relapse. Therefore, the existing drugs are not ideal, far from satisfying the needs of patients. It is thus indeed imminent to develop new drugs with fast onset of action, broad antidepressant spectrum and less toxic and side effects, which will bring great social and economic benefits to the society as well.
Cordycepin, as the main active ingredient of cordyceps militaris (especially nucleosides), is the first nucleoside antibiotic isolated from the fungus. Cordycepin is a kind of adenosine analogue (3′-deoxyadenosine), whose molecular formula is C10H13N5O3, molecular weight 251.24, melting point 230° C.˜231° C., alkaline, in the form of acicular or flaky crystal. Its molecular structure is shown in FIG. 1.
The medical effects of cordycepin have been reported, among which the effects in such aspects as anti-inflammation, anti-microbial, anti-virus and anti-tumor have been proved by more and more clinical and basic experiments. It is found based on research that, cordycepin can be antagonistic to the generation of NO product, so cordycepin is likely to become a drug for the treatment of disorders caused by inflammation. At the same time, cordycepin can act as a broad-spectrum antibacterial to inhibit the growth of many pathogenic bacteria like streptococcus, actinobacillus mallei, bacillus anthracis, swine hemorrhagic bacillus septicaemiae and staphylococcus. Cordycepin also has inhibitory effects on bacillus subtilis and skin pathogenic fungus such as microsporum gypseum, microsporon lanosum and sycosis ringworm fungi. In addition, cordycepin has fairly strong antiviral activity. What's more, some other studies have showed that cordycepin can resist herpes virus and inhibit encephalitis virus as well as HIV-I type infection of human immunodeficiency virus. In recent years, researchers have found that cordycepin shows immunomodulatory effects. Besides, cordycepin can promote T lymphocyte transformation, improve the phagocytosis of mononuclear macrophage system, and activate macrophages to produce cytotoxin to directly kill cancer cells. As cordycepin can interfere with the synthesis of RNA and DNA in gene cells, inhibit cancer cell division, be used as the tool to distinguish different RNA polymerases in cells, and possess the special efficacy of repairing gene cells and protecting genetic codes, it can be used as a nucleoside drug. In 2000, American NCI researchers and the professor from School of Medicine of Boston University jointly confirmed based on study that cordycepin has very good curative effects on leukemia.
Among numerous reports of animal experiments or clinical trials above, the curative effect of cordycepin on depression has not yet been reported, and no instance of treating depression by cordycepin is mentioned.